354 STUDIES IN GENERAL PHYSIOLOGY 



about in the vessel during the night, and came to rest in the 

 morning in the darkest regions. 



These animals possess at the oral pole not only a brain 

 but also comparatively well-developed eyes. I decided to 

 test whether a decapitated Planarian still shows the same 

 reactions toward light as normal Planarians, in spite of the 

 loss of brain and eyes. This is true in a most surprising 

 way. About sixty specimens of Planaria torva were cut 

 across transversely, close behind the brain and the eyes, in 

 the evening. All the pieces were put into a vessel having 

 vertical sides and half covered with black paper. On the 

 next morning nearly all the posterior pieces as well as the 

 oral pieces were found in the covered part of the aquarium. 

 They were fairly uniformly distributed here. A few were 

 found in the uncovered portion of the vessel, but among 

 these there were head pieces as well as aboral pieces crowded 

 together in one corner in the room side of the dish. In this 

 corner the intensity of the light was relatively low. In 

 repeating this experiment with normal animals I obtained 

 the same results as with the decapitated animals. When the 

 decapitated animals had collected in the covered portion of 

 the vessel and had become perfectly quiet, their quiet was 

 quickly disturbed when the dark paper was suddenly removed 

 without jarring the vessel. The animals began to move, crept 

 at first toward the room side, and finally collected again in 

 regions where the light was least intense. This reaction also 

 occurred as in normal animals, with this difference, however, 

 that the reaction time of the brainless animals to changes in 

 the intensity of the light was greater than in normal animals. 

 In the animals possessing a brain and eyes the reaction began 

 about one minute after light struck them; in the brainless 

 pieces after about five minutes. In these experiments only 

 diffuse daylight was used as a stimulus. 



I have pointed out before that when uninjured Planarians 



